The present invention relates generally to an hybrid electric vehicle (HEV), and specifically reducing torque reversals during throttle back-out transmission up-shifts in an HEV.
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a parallel/series xe2x80x9csplitxe2x80x9d configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, a generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge a battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
In each of the HEV powertrain configurations described above, the generator motor can be used as the starter motor for the ICE. When the generator motor performs this combined function, the generator can be referred to as a combined starter/alternator (S/A) or an integrated starter/generator (ISG).
The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or driveability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shutdown. Nevertheless, new ways must be developed to optimize the HEV""s potential benefits.
One such area of HEV development is improving vehicle driveability, specifically improving the response of the HEV to changes in throttle position, particularly, throttle back-outs. A throttle back-out occurs when the throttle is released from an open position to a closed position. Throttle position is typically measured in a percentage, where 100% throttle represents a wide-open throttle and 0% throttle represents a closed throttle. During a throttle back-out, the vehicle transmission may need to up-shift, i.e., shift to a higher gear, so as to not provide an undesirable amount of negative torque to the vehicle.
While most HEVs include a transmission, either manual or automatic, in the driveline, many HEVs do not have a hydraulic torque converter between the engine and the transmission. In these HEVs, the clutches and gears between the engine, traction motor, generator motor and transmission must perform the function of the conventional hydraulic torque converter to not only transfer torque through the driveline, but also provide a measure of damping during gear shifts.
Gearshift control of transmissions and transmission controls in an HEV are known in the art. Brown et al., U.S. Pat. No. 5,596,495, discloses a system for controlling a down-shift in an automatic transmission having a torque converter. Brown et al., U.S. Pat. No. 6,176,808 discloses a hybrid vehicle powertrain and controller. The 808 patent discloses a powertrain assembly for an automotive vehicle having an internal combustion engine and transmission for delivering engine torque to traction wheels of a vehicle. An electric induction motor is situated in the torque flow path between the engine and the transmission. The induction motor supplements engine torque, permitting the engine to be turned off when the vehicle is at rest, thereby improving fuel economy and reducing undesirable exhaust gas emissions from the engine. Here, torque multiplication that would normally be available from the hydrokinetic torque converter in the transmission is essentially replaced by the induction motor during vehicle startup. A vibration damping function of the hydrokinetic torque converter during engine idle is also performed by the induction motor, again eliminating the need for a hydrokinetic torque converter. The induction motor, during operating modes where induction motor torque is not required, functions as an alternator during periods of regenerative braking, when the internal combustion engine is inactive and when the vehicle is in coast mode.
Fujisawa et al., U.S. Pat. No. 6,175,785, discloses a hybrid vehicle that is driven by either an engine or a motor by tightening or releasing a clutch interposed between an engine and a transmission. A generator is connected to the engine, and engine torque is absorbed by the generator when the power source is changed over from the motor to the engine. The clutch is tightened when the rotational speed of the motor and the engine coincide. As a result, the torque input to the transmission is maintained constant, and shock due to changeover of the power source is suppressed.
Lawrie, U.S. Pat. No. 5,979,257, discloses a powertrain system for a hybrid vehicle that includes an engine and an electric machine, which operates as both an electric motor and an alternator, to power the vehicle. The hybrid vehicle also includes a manual-style transmission configured to operate as an automatic transmission from the perspective of the driver. The engine and the electric machine drive an input shaft, which in turn drives an output shaft of the transmission. In addition to driving the transmission, the electric machine regulates the speed of the input shaft in order to synchronize the input shaft during either an up-shift or down-shift of the transmission by either decreasing or increasing the speed of the input shaft. When decreasing the speed of the input shaft, the electric motor functions as an alternator to produce electrical energy, which may be stored by a storage device. Operation of the transmission is controlled by a transmission controller that receives input signals and generates output signals to control shift and clutch motors to effect smooth launch, up-shifts and down-shifts of the transmission, so that the transmission functions substantially as an automatic transmission from the perspective of the driver, while internally substantially functioning as a manual transmission.
While HEV controls are known in the art, none are known that can reduce torque reversals during throttle back-out transmission up-shifts.
Accordingly, the present invention provides a strategy that uses a generator motor to reduce torque reversals during throttle back-out transmission up-shifts in an hybrid electric vehicle (HEV).
One aspect of the invention is the use of a generator motor to maintain engine speed to prevent torque reversal, i.e., driving of the engine by the transmission, during up-shifts of the transmission when the throttle is being released. A related aspect relates to determination, using a controller, of the engine speed at the time the transmission shift is being entered. The controller commands the generator motor to hold this engine speed for a time sufficient to enable the shift to occur, thus avoiding disagreeable negative torque and vehicle deceleration. In accordance with a further related aspect of the invention, the generator motor is operated in a closed-loop control mode resulting in abatement of negative torque and enabling smooth shifting. The generator motor can also operate in an open-loop control mode, also resulting in abatement of negative torque and enabling smooth shifting. Open-loop control can use look up tables or other control methods known in the art.
Briefly, the invention provides a strategy and system for an hybrid electric vehicle (HEV) that is not equipped with a hydraulic torque converter wherein a generator motor is utilized to maintain engine rotational velocity during up-shifting of the vehicle especially in situations where the throttle of the engine is quickly released. A controller adapted to control the generator motor is supplied with data output by detectors that monitor the rotational velocity of the engine and the gear ratio of the transmission. The controller is programmed to command the generator motor to maintain the rotational velocity of the engine above a preselected threshold during up-shifting of the transmission.
Other features and advantages of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.